Build the site to see the instructions for using it. Or just go here: http://idratherbewriting.com/documentation-theme-jekyll/

You can also use Docker to directly build and run the site on your local machine. Just clone the repo and run the following from your working dir:

docker build --no-cache -t mydocs .

Once the build is complete, you can mount and run the whole site as follows:

docker run -v "$PWD:/src" -p 4000:4000 mydocs serve -H 0.0.0.0

This is perhaps the easiest way to see how your site would actually look.